1. Field of the Invention
The present invention relates to an ignition appliance for a heat generator, comprising a fuel gas supply passage, an air supply passage, a flame tube and an igniter, the igniter being arranged in an ignition space through which flow occurs and which is spatially remote from the flame tube, which ignition space opens into the flame tube.
2. Discussion of Background
The ignition of flames in heat generators, as for example in gas turbine combustion chambers, can take place for example by means of an igniter plug or a glow plug, as described inter alia by A. Lefebvre in "Gas Turbine Combustion" (Arthur H. Lefebvre: Gas Turbine Combustion, Hemisphere Publishing Corporation, 1983).
An obvious precondition for the function of the ignition appliance is that conditions are present at the igniter which are essential for a stable and sufficiently powerful ignition flame to occur in the first place. In this connection, particular mention should be made of the setting of the fuel/air ratio at the igniter and of an appropriate flow velocity in the region of the igniter.
These requirements can often only be satisfied by the employment of special ignition burners, particularly in the combustion chambers of gas turbines. Placing the igniter directly in the combustion space is intrinsically ruled out by the criteria mentioned above. The igniter is therefore frequently accommodated in a small ignition space so that only a small volume has to be ignited by the initial ignition. A stable ignition flame occurs in succession in a flame tube located downstream of this ignition space. Even then, satisfactory results are often only obtained with substantial complication, for example by the employment of ignition gas supply systems fed with propane gas.
If, on the other hand, direct ignition is to take place with natural gas or even with low calorific value gases, the range of fuel/air ratios in which a reliable function is ensured is very tightly limited. The gas supply and air supply to the igniter must correspondingly have very tight tolerances and the upstream gas pressure must be carefully matched.
Under the conditions which are present in the combustion chambers of modern gas turbines, the ignition systems demand a high level of maintenance in order to maintain their reliable function over a long period of time.